It is known that, in about 30% of patients with hemophilia A and B, an antibody against the FVIII (factor VIII) or FIX (factor IX) protein used for treatment is produced to significantly reduce the therapeutic effect of the protein. As an alternative to the protein, activated factor VIIa or aPCC (plasma-derived activated prothrombin complex concentrate) has been administered.
The above-described recombinant protein is administered to hemophilia patients by intravenous injection twice or more a week, but inconvenience caused by repeated administration of the recombinant protein has been constantly presented. Thus, studies on long-acting recombinant proteins having an increased half-life have been actively conducted.
In hemophilia models, an approach against TFPI (tissue factor pathway inhibitor) has recently been attempted. TFPI is involved in the extrinsic pathway of blood coagulation, and functions to inhibit blood coagulation by preventing factor X activation with TF/FVIIa (see FIG. 1). Thus, when TFPI is inhibited by an anti-TFPI antibody, blood coagulation during bleeding can be activated by the extrinsic pathway.
TFPI consists of three KPI domains (Kunitz-type domains or Kunitz domains), and KPI-2 (Kunitz domain 2) inhibits FXa by binding directly to FXa (see FIG. 2). This means that KPI-2 forms a complex of TF/FVIIa/FXa/TFPI, resulting in direct inhibition of production of FXa.
An anti-TFPI antibody may be used in patients in which an antibody against the FVIII or FIX protein has been produced. In addition, the anti-TFPI antibody has a very long half-life (about 2 weeks), and thus the number of administrations thereof can be reduced.
Hemophilia therapeutic agents against TFPI are mostly in the research stage or the initial development stage. For example, the humanized monoclonal antibody (mAb) mAb2021 developed by Novo Nordisk is a humanized antibody (IgG4) that is an anti-TFPI monoclonal antibody, and is in the phase 1 clinical stage. In addition, ARC19499 developed by Baxter is a PEGylated aptamer targeting TFPI and is in the preclinical stage. Furthermore, JBT2329 developed by Baxter & 3B Pharmaceuticals is a Pegylated anti-human TFPI 20mer peptide and is in the preclinical stage.
The need for a new agent for treating hemophilia has been constantly proposed, and the development of therapeutic agents that are approaches other than a bypassing agent such as FVIIa is urgently required. In particular, an approach to a drug that inhibits the TFPI pathway is preferred. Among hemophilia patients who are administered with a blood coagulation factor, a number of patients having resistance to the factor exist, and thus require a new drug. However, medical issues such as antigen (Ag)-antibody (Ab) complex clearance should be taken into consideration.
Accordingly, the present inventors have made extensive efforts to develop a novel antibody that binds specifically to TFPI, and as a result, have found that the use of the antibody can activate the extrinsic pathway of blood coagulation by inhibiting the anticoagulation mechanism of TFPI, thereby completing the present invention.